Fully grounded pressure switch

ABSTRACT

The pressure switch has a switch mounted in the plastic, electrically insulative case above the diaphragm. The perimeter of the diaphragm is captured between the plastic case and the cup which has a tubular connector for connection to a source of pressure to be sensed. The chamber below the diaphragm between the diaphragm and cup is the pressure chamber and pressure variations cause flexure of the diaphragm and operation of the switch. The rim of the cup is rolled over the case flange to hold the parts assembled. The mounting bracket is secured to the case and to the appliance (or other equipment) frame - which is electrical ground - and, therefore, satisfies more stringent electrical requirements. In order to ground the cup - even though it is electrically dead - one end of a conductive ground strap is captured between the case and the cup when the cup rim is rolled over the case flange. The other end overlies the bracket and is captured by a screw mounting the bracket to the case. The arrangement meets demanding electrical requirements at very low cost and without requiring added costy manufacturing operation.

United States Patent n91 Gebel et al.

[ Mar. 19, 1974 FULLY GROUNDED PRESSURE SWITCH [75] Inventors: IrvingGebel, Oak Park; Abed G.

' Kahale, Roselle, both of Ill.

[73] Assignee: Controls Company of America,

Schiller Park, Ill.

[22] Filed: Mar. 16, 1973 [21] Appl. No.: 341,911

[52 US. Cl. 200/83 R, 200/83 WM [51] Int. Cl H0111 35/34, HOlh 9/12 [58]Field of Search 200/83 R, 83 WM, 83 B,v

[56] References Cited UNITED STATES PATENTS 3,315,053 4/1967 BauerZOO/83 WM [57] ABSTRACT The pressure switch has a switch mounted in theplastic, electrically insulative case above the diaphragm. The perimeterof the diaphragm is captured between the plastic case and the cup whichhas a tubular connector for connection to a source of pressure to besensed. The chamber below the diaphragm between the diaphragm and cup isthe pressure chamber and pressure variations cause flexure of thediaphragm and operation of the switch. The rim of the cup is rolled overthe case flange to hold the parts assembled. The mounting bracket issecured to the case and to the appliance (or other equipment) framewhich is electrical ground and, therefore, satisfies more stringentelectrical requirements. In order to ground the cup even though it iselectrically dead one end of a conductive ground strap is capturedbetween the case and the cup when the cup rim is rolled over the caseflange. The other end overlies the bracket and is captured by a screwmounting the bracket to the case. The arrangement meets demandingelectrical requirements at very low cost and without requiring addedcosty manufacturing operation.

1 Claim, 2 Drawing Figures 1 FULLY GROUNDED PRESSURE SWITCH BACKGROUNDOF THE INVENTION Pressure switches of the general type shown herein havebeen considered electrically safe since all terminals and switchelements are mounted on insulative plastic. The pressure switch ismounted on the equipment frame by means of a metal bracket. UnderwritersLaboratories now proposes that all metal parts be grounded even thoughelectrically dead. The end cup in a pressure switch is such a dead metalpart and thus requires grounding, notwithstanding the fact that itboggles the imagination to conceive of a failure which couldtresultinvthe cup becoming electrically live. Obviously any part can begrounded but the problem is to do so at low cost and withoutjeopardizing the basic reliability of the pressure switch.

SUMMARY OF THE INVENTION The provision of the grounding strap having oneend captured between the metal cup and the plastic case with the otherend connected to the mounting bracket provides an extremely simple andlow cost solution to the problem of meeting the new standards. Theconstruction does not impair the diaphragm seal and thus cannot affectthe pressure switch performance. No added costly manufacturingoperations are required. The piece part cost is minimal. Other proposedsolutions were not satisfactory for cost or performance reasons. Thepresent solution easily meets the standards (two-volt maximum drop underoverload conditions of 40 amps for two minutes and a surge of 1,000 ampsat 250 volts without appreciable galvanic corrosion or structuralimpairment).

- DESCRIPTIONS OF THE DRAWINGS FIG. 1 is a perspective view of thepressure switch according to this invention.

FIG. 2 is a vertical section taken along a longitudinal line showing theinternal construction of the pressure switch.

DESCRIPTION OF THE PREFERRED EMBODIMENT The pressure switch has aplastic, non-conducting case and a bottom metallic cup 12 sandwichingand gripping the rim of the diaphragm 14 between the case and the cup,the upstanding rim 16 of the cup being crimped or rolled over the flange18 of the case. The cup has a tubular connector 20 welded thereinaffording means for introducing pressure variations into the chamber 22below the diaphragm so the diaphragm may flex in accordance with thepressure in the chamber. The diaphragm is provided with a rigiddiaphragm pad 24 with an upstanding actuator 26 acting on the tongue 28of the switch 30. The switch has a contact supporting blade 32 which isinterconnected with the tongue by means of the barrel spring 34imparting overcenter action to the blade 32 between lower contact 36 andthe upper contact 38. The actuator 26 is opposed by spring 40 compressedbetween seat 41 and plunger 42 which is positioned by lever 44controlled by cam member 46 fixed on shaft 48 and actuated by lever 50which is adapted to project through the front of a splash panel on awashing machine, for example. Details of such construction are notimportant here nor are the details of the switch actuation. It isnecessary only to appreciate that the switch 30, the switch blade andthe two contacts are connected to terminals 52, 54, 56 on the exteriorof the case.

Bracket 58 is secured to the case by screws 60, 62 and serves to supportthe pivot 48 for the cam member 46 and is provided with tabs 64, 66which are adapted to be secured to the machine frame which, in machinesof this type, is considered electrical ground. The bracket 58 is, ofcourse, an electrically dead member and complies with the new standardsfor grounding dead metal parts.

The problem solved by this invention is the requirement that theelectrically dead metal cup 12 must now be grounded. One can conceive ofmany methods of accomplishing this including redesigning the cup,electrically conductive paint on the case, etc. but the solutionprovided by this invention represents simplicity in itself and yet hasproven highly satisfactory by way of meeting the functional andelectrical requirements at extremely low cost. Thus the grounding strap68 has one end positioned between case flange 18 and rim 16 prior to therim being crimped or rolled onto the flange. Thus when the rim iscrimped onto the flange, the lower end of the strap 68 is mechanicallyclamped between the case flange 18 and rim without adverse effect on theseal at the diaphragm. Preferably a copper strip is used to takeadvantage of the high electrical conductivity and easy forming. Thestrap is formed with a sharp bend 70 to reduce precision required informing this part. The screw hole in the secured end 72 of the strap caneasily be positioned over the corresponding hole in the mounting bracket58 and, of course, in the case 10. Then when the screw 62 is tightened,the strap 68 is securely mounted on the pressure switch providing a goodelectrical path between the cup 12 and the metal bracket 58 and, hence,to the machine frame when the switch is in its operating environment.This meets all requirements of the new standards, which standards areapplicable even though it is difficult to see how a rather substantialdisintegration of the switch itself could result in the cup becomingelectrically conductive since all the switch parts are insulated fromthe cup by the rubber diaphragm. A more probable hazard, albeit mostunusual, would be some sort of short between a terminal (52, 54, 56) andthe cup.

We claim:

1. A pressure switch including a non-conducting case,

a conductive cup secured to the case,

a diaphragm having its periphery captured between the case and cup toprovide a pressure chamber between the diaphragm and cup,

a switch mounted in the chamber between the case and diaphragm,

a conductive mounting bracket secured to the case,

said cup including a rim and being secured to the case by crimping therim onto the case,

an electrically conductive grounding strap having one end capturedbetween the rim and case and secured thereto when the rim is crimpedonto the case, I

the other end of the grounding strap being connected to said conductivebracket, said strap bridging the portion of the case lying between thetwo points of connection of the strap.

m s =0 1: t

1. A pressure switch including a non-conducting case, a conductive cupsecured to the case, a diaphragm having its periphery captured betweenthe case and cup to provide a pressure chamber between the diaphragm andcup, a switch mounted in the chamber between the case and diaphragm, aconductive mounting bracket secured to the case, said cup including arim and being secured to the case by crimping the rim onto the case, anelectrically conductive grounding strap having one end captured betweenthe rim and case and secured thereto when the rim is crimped onto thecase, the other end of the grounding strap being connected to saidconductive bracket, said strap bridging the portion of the case lyingbetween the two points of connection of the strap.